Equipment for promoting economical and safe loading of aircraft



E. KOLISCH Aug. 17, 1954 EQUIPMENT FOR PROMOTING ECONOMICAL AND SAFELOADING OF AIRCRAFT 5 Sheets-Sheet 1 Filed Feb. 26, 1952 INVENTQR Elia]lfolz'sch BY WJWMMOM ATTORNEYS mv Q ||||l Ill lllilllll I l I I l l I ll I l I ll.

mm mm Aug. 17, 1954 E. KOLISCH EQUIPMENT FOR PROMOTING ECONOMICAL ANDSAFE LOADING OF AIRCRAFT 5 Sheets-Sheet 2 Filed Feb. 26, 1952 INVENTOREm z'i K0125171 1 ATTORNEYS Aug. 17, 1954 E. KOLISCH EQUIPMENT FORPROMOTING ECONOMICAL AND SAFE LOADING OF AIRCRAFT 5 Sheets-Sheet 3 FiledFeb. 26, 1952 mk NNN il-l Al A

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EQUIPMENT FOR PROMOTING ECONOMICAL AND SAFE LOADING OF AIRCRAFT FiledFeb. 26, 1952 5 Sheets-Sheet 5 ls. ig.5.

having a nose wheel and a pair of main wheels,

Patented Aug. 17, 1954 UNITED STATES PATENT OFFICE EQUIPMENT FORPROMOTING ECONOMICAL AND SAFE LOADING OF AIRCRAFT Emil Kolisch, NewYork, N. Y., assignor to Continental Silver 00. Inc., Brooklyn, N. Y., acorporation of New York Application February 26, 1952, Serial No.273,493 15 Claims. (Cl. 235-61) 1 2 As conducive to an understanding ofthe in- DRMW=the distance from the nose of the center vention, it isnoted that in order for an airof the right main wheel when projectedupon craft to take off, fly and land safely, its center the longitudinalaxis of the aircraft.

of gravity along the tength of t plape must The center of gravity may bedetermined more be at some predetfermnged. g g i. 2 may simply by usingthe main wheels as the reference Vary between 93 de i Xe mu datum. Thequotient of the product of weight These permlsslble fixed hmnfs aredetelimmfad on the nose wheel by its distance from the main by hmanufacturer of the alrcraft ordmamy wheels divided by the total weightof the plane by flight tests, and are generallyexpressed with gives theprojection upon the longitudinal axis respect'to the mean aerodynamlchere 10 of the aircraft of the distance of the center inafter designatedMAC, The MAC 0 an aircraft is described in text books as the chord of ofgravlty from the center of the mam Wheels an air-foil, which isgenerally a definite segment fi f may be expressed by the between theleading and trailing edges of the wing. CG: WNWXDNW The distance of thecenter of gravity of an WNW+WLMW+WRMW aircraft from a fixed referencedatum is equal to the total moment of such aircraft about such m whlchreference datum divided by its total weight. CGzdistance of center ofgravity from main Where the nose of the aircraft is selected as thewheels. reference datum, and the aircraft is of the type WNWzWeight o oswhe l,

DNWzdistance of the nose wheel from the centhe distance of each wheelfrom the nose along ter of th main wheels when projected upon the lengthor longitudinal axis of the aircraft is the longitudinal axis of theaircraft. multiplied by the Weight o the espo d n 5 WLMW=weight on leftmain wheel. wheel to determine the respective moments about WRMWzWeighton right m i h l, the nose. The sum of these moments is divided by thesum of the three weights to determine the To illustrate the two formulasabove-mendistance of the center of gravity from the nose. tioned, let itbe assumed that the nose wheel of such calculations may be expressed bythe an aircraft is 100 inches from its nose and carformula: ries aweight of 10,000 pounds and the two main (WNWXDNW)+(WLMW DLMW)+(WRMWDRMW) WNW+WLMW+WRMW in which wheels are 430 inches from the nose andeach CG=distance of center of gravity from nose of 4 carries a weight of30,000 pounds.

aircraft. In the first formula we find:

WNW=weight on nose wheel. In the second formula for CG, we find:

DNW=the distance from the nose of the center of the nose wheel whenprojected upon the (2) G= =47.14 longitudinal axis of the aircraft. ii000+ 0,000 WLMW=weight on left main wheel. As the center of gravitydetermined by the DLMW the distance from the nose of the cenfirstformula utilized the nose of the aircraft as ter of the left main wheelwhen projected upon the reference datum, the value determined, i. e.,the longitudinal axis of the aircraft. 382.86 inches, is the distance ofthe center of .WRMWzweighb n ri ht; main wheeL gravity from the nose. Inthe second formula 3 the main wheels were used as the reference datumand the value of 47.14 inches in the direction of the nose wheel is thedistance of the center of gravity from the main wheels. As the distancefrom the nose of the aircraft to the main wheels is equal to 430 inches,it is apparent that regardless of which formula is used, the center ofgravity will be at the same location, i. e., 382.86 inches from the noseof the aircraft.

Assuming that the aircraft, after the center of gravity has beendetermined, as above described, is loaded with an additional weight of1,000 pounds at a point 200 inches from its nose, the new center ofgravity as thus loaded may be determined by the following formula:

( CG (C'GXweight) (added weightXarm) 1 Weight-l-added weight If the noseof the aircraft is utilized as the reference datum:

cGl distance of new center of gravity from nose of aircraft.arm=distance of added weight from nose of aircraft.

If the main wheels are used as the reference datum:

Utilizing formula 3 for each reference datum:

Utilizing as the reference datum, the main wheels which are 430 inchesfrom the nose of the aircraft, the permissible limits of the MAC will bebetween 30 and 50 inches from the main wheels; the minus sign allowingfor the fact that the measurements of H and Y are in the negative orforward direction:

According to one present practice, the basic weight of an aircraft, i.e., without fuel, crew, safety equipment or cargo, but including allstandard equipment, is determined generally by actually weighing theaircraft on suitable scales. The basic center of gravity is thencalculated by utilizing suitable formulas such as Formulas 1 or 2 abovedescribed.

Assuming that the aircraft is to travel to a pre-' determineddestination requiring a given fuel load, the weight of which is readilyascertainable, a specialist in the Weights and Balances Division of anairport, taking into consideration the basic weight and basic center ofgravity of the aircraft as well as the weight of the crew, fuel andsafety equipment and the locationof such items, may determine a standardcalculating device, such as a slide rule which is well known to thoseskilled in the art, the initial center of gravity of the aircraft.

(382.86 X70,000) (1,000X200) :380-28 inches from nose The center ofgravity of an aircraft with respect to any given reference datum mayalso be expressed in terms of percent MAC which is the ratio of thedistance of the center of gravity from the leading edge of the MAC tothe width of the MAC multiplied by 100.

The percent MAC may be determined by using the formula:

CG in percent MAC= 100 in which H=distance from reference datum tocenter of gravity. Y=distance from reference datum to leading edge ofMAC. C=width of MAC.

and selecting as the center of gravity the rearward limit of the MAC Thepayload or weight of cargo is of course the permissible gross take offweight less the basic weight of the aircraft, fuel, crew and safetyequipment.

According to the present practice, the cargo loading supervisor attemptsto distribute the cargo, including passengers, along the length of theaircraft so that the final center of gravity of the fully loadedaircraft will fall within the permissible limits of its MAC.

Generally the heaviest cargo is loaded into a compartment which isadjacent to or between the permissible limits of the MAC. The weight ofthe successive items of cargo, generally indicated on each item by theshipper or manufacturer, and their position in the aircraft are noted onthe manifest as the loading proceeds.

After the aircraft has been loaded, the manifest is turned over to theWeights and Balances Division of the airport, which transfers the dataon the manifest to a slide rule which indicates the final or take offcenter of gravity of the aircraft as thus loaded.

loaded.

Inasmuch as it is essential that the final center of gravity of theloaded aircraft be within the permissible limits of the MAC for safetake off, flying and landing of the aircraft, the personnel of theWeights and Balances Division must be highly trained and must performtheir work with extreme care, for any errors in their calculations mighthave fatal consequences. As a result, the calculations of the Weightsand Balances. Division must be carefully checked and re-checked forerrors and even with such checking, by reason of the human elementinvolved, there is no assurance that some error has not remainedundetected.

Inasmuch as the subsequent settings of the slide rule to determine thefinal center of gravity of the loaded aircraft depends upon the accuracyof the basic center of gravity determination thereof, if any items ofequipment should be added to or removed from the aircraft withoutappropriate entries and calculations being made of the weight added orremoved and the location of such weight, no matter how accurately thesubsequent settings on the slide rule are made for the initial center ofgravity determination with respect to crew members, fuel and safetyequipment and the final center of gravity determination with respect tocargo, such slide rule determined final center of gravity may differmaterially from the actual final center of gravity of the aircraft.

Even if all items added to or removed from the aircraft are properlylisted and calculated, due to extraneous factors present at the time oftake oil, the slide rule determined final center of gravity of theaircraft may in fact not be its actual final center of gravity. Thus,for example, if the aircraft has been carrying cargo such as coal, thecollection of coal dust in the crevices oi' the aircraft, especiallynear the tail end, may add such a moment that the final center ofgravity determined by the slide rule, though within the permissiblelimits of the MAC, is misleading because the actual center of gravitymay in fact be outside of such limits. As a result, the aircraft may betail-heavy, with resultant possibility of crash on take off. Inaddition, such factors as collection of moisture on the surfaces of theaircraft before take off may add a moment that also will cause theactual final center of gravity at time of take off to differ from theslide rule determined center of gravity with resultant possibility ofcrash or uneconomical fuel consumption during flight.

In addition to the reasons above given for the deviation of the sliderule determined final center of gravity from the actual final center ofgravity, it is very possible that the weights of the items of cargo usedin the calculations, if taken from the suppliers markings on such items,may be inaccurate and such inaccuracy might also cause the actual finalcenter of gravity of the aircraft to differ from the slide ruledetermined final center of gravity with resultant possible fatalconsequences.

Moreover, as fuel is consumed by the aircraft in flight, the center ofgravity of such aircraft may shift and may not be within the limits forsafe landing.

It is accordingly among the objects of the invention to provide a methodand equipment which may readily be operated by even an unskilledpersonand which will automatically take into account the actual weightof the loaded aircraft and theactual position of the contents thereofwithout error due to erroneous marking of weights on the items of cargoloaded into the aircraft, erroneous entries on the manifest of weight orposition, omissions in entry or elimination of items of equipment addedor withdrawn respectively from the aircraft or the accumulation of dust,dirt or moisture, and will quickly and accurately indicate the actualfinal center of gravity of the aircraft, in order to facilitate checkingthat it is within the permissible limits set by the manufacturer forsafe take off, flying and landing, all without need for time-consumingcalculations or manipulations of any sort and the possibility of humanerrors is completely eliminated.

Another object is to provide a method and equipment by which the actualposition of center of gravity may be observed at all times as theloading proceeds, so as to dispense with the need for extensive shiftingof the cargo in a fully loaded plane which may become necessary toassure safety when such guidance is not afforded.

Another object is to provide a method and equipment of the above typewhereby, once the actual final center of gravity has been determined,the center of gravity of such aircraft at time of landing may beautomatically ascertained with but a single simple manipulation based onthe weight reduction during flight to a given destination.

It has been found that during weighing of an aircraft in the open, evenon a relatively calm day, the force of the wind directed longitudinallywhether from front to rear or rear to front of the aircraft, causes theweight indication on the scales to deviate from the actual weight of theaircraft. Where, however, the wind is directed laterally of theaircraft, its effect upon the weight indication is negligible.

It is accordingly another object of the invention to provide a methodand equipment of the above type which will permit ready determination ofthe weight data with the aircraft positioned transversely of thedirection of the wind and yet without the need for shifting or adjustingthe weighing equipment or accessories thereof regardless what thedirection of the wind.

According to the invention from its broader aspect, the equipmentcomprises facilities whereby the weight factor is introduced in responseto the weight on the respective wheels to regulate an electric impulserelated thereto. The equipment also comprises facilities to regulate anelec tric impulse related to the total moment of such aircraft withrespect to any given reference datum. The electric impulses areconnected in suitable circuits so as to give an indication equal to thetotal moment divided by the total weight or the distance of the centerof gravity from the reference datum.

In a preferred application of the invention, a pair of currentregulating means is actuated by each of the three wheels conventionallyused on aircraft, the current regulating means of each pair beingrelated respectively to the weight on the associated wheel and thedistance of such wheel from any selected reference datum. The threepairs of current regulating means are connected in suitable circuits togive a response corresponding to the sum of the products of the weighton each wheel multiplied by its distance from the selected referencedatum or the total moment of the aircraft with respect thereto.

Facilities are provided to set into circuit with .such three pairs ofcurrent regulating means.

additional current regulating means related to the sum of the weights onsuch three wheels. The current regulating means are connected insuitable circuits so as to give an indication equal to the total momentdivided by the total weight or the distance of the center of gravity ofthe aircraft from the selected reference datum.

To this end, in a specific application of the invention, the currentthrough resistance of value proportional to the logarithm of the totalmoment of the aircraft with respect to a given reference datum isopposed by current from a common source through resistance of valueproportional to the logarithm of the total weight of the aircraft. Thequotient of the total moment divided by the total weight is obtainedfrom a variable logarithmic resistance in series with the total weightresistance and said variable resistance is operated preferably by amotor drive controlled by the resultant difierence of potential untilsuch difference is eliminated, whereby a suitable scale associated withsaid variable resistance will indicate the quotient of moment divided byweight or the distance of the center of gravity from the referencedatum.

The total moment resistance desirably forms one leg of a Wheatstonebridge and the series connected total weight resistance and variableresistance form another leg, the motor drive being controlled by theoutput of the bridge until the latter is balanced.

In the accompanying drawings in which are shown one or more of variouspossible embodiments of the several features of the invention,

Figs. 1 and 2 are circuit diagrams of one embodiment of the equipment,

Fig. 3 is a circuit diagram of another embodiment thereof,

Fig. 4 is a circuit diagram similar to Fig. 3 with a wind compensatorcircuit added thereto.

Fig. 5 is a front elevational view with parts broken away of a typicalsupporting panel,

Fig. 6 is a longitudinal sectional view taken along line 6-6 of Fig. 5of a typical indicating drum and drive motor,

Fig. 7 is a diagrammatic front elevational view of an indicating scale,

Fig. 8 is a longitudinal sectional view taken along line 83 of Fig. '7,and

Fig. 9 is a transverse sectional view taken along line 99 of Fig. '7.

In order to simplify the description of the circuit and operation of theequipment, it will be assumed that the equipment is designed to measurethe center of gravity of two types of aircraft, type A and type B, eachillustratively having two main wheels and a third wheel which may be anose wheel, it of course being understood that the equipment and circuitcould readily be modified to measure any number of types of aircraft.

In the equipment shown in Figs. 1 and 2 of the drawings, three momentsare utilized to determine the center of gravity, 1. e., the moment ofthe weight on each wheel with respect to a reference datum,illustratively the nose of the aircraft.

The equipment utilizes a plurality of substantially identical Wheatstonebridge circuits. Each bridge circuit has a pair of balancing resistances2i and 22 connected at one end to corresponding points 23 and 24 withthe other ends of said resistances connected to corresponding negativemain 25. A servo-amplifier 26 connected by input leads 21 and '28respectively, to points 23 and 8 24 of each bridge is connected by lead29 to a servo-motor 3|. The servo-motor and servo-amplifier areillustratively of the type put out by the Brown Instrument Division ofthe Minneapolis- Honeywell Regulator Company under the designation BrownEl'ectronik continuous balance unit No. 354,574.. As shown in Figs. 1,2, 5 and '6, the servo-motor 31 is operatively connected by means of ashaft 32 to a rotatable member, desirably a drum 33 which carries wipermeans thereon to contact resistances and conducting rings on anassociated insulating panel 34 so that depending upon the position ofthe drum and the wiper arm, a predetermined amount of resistance may beplaced in circuit.

The equipment desirably comprises a plurality of weighing scales of anysuitable type, three weighing scales being illustratively provided,designated by the numerals 35, 36 and 31, to measure the weight on thenose wheel and two main wheels respectively.

In the illustrative embodiment herein shown, each scale controls a setof three movable contact arms 38, 39, 4!; 42, 43, M and 45, 46, 4?,respectively which coact with an associated resistance bank 48, 69, El;52, 53, 54 and 55, 55, 51 respectively to place in circuit that portionof the associated resistance bank related to the value of the weightbeing measured.

The movable arm 38 of one of the scales, i. e., scale 35, is connectedby lead 58 to positive main 59. One end of resistance bank 48 isconnected by lead 6! to movable arm 42 of scale 36 and one endof'resistance bank 52 is connected by lead 62 to movable arm 45 of scale31. Thus, the resistances 48, 52 and 55 are connected in series.

One end of resistance bank 55 is connected by lead 63 to point 24 ofWheatstone bridge 54.: .Point 23 of bridge 64 is connected by lead 65 toone end of resistance bank 66, desirably a. continuous length of wiremounted on insulating supporting panel 34 associated with bridge 64,said resistance desirably being arranged as an annulus. Also .mounted onpanel 34 concentric with resistance bank 56 and desirably encompassedtherebyis a conducting ring ill, a second annular resistance bank 58 anda second conducting ring 69. The conducting rings 61 and 69 are bothdesirably connected to positive main 59 and one end of resistance bank38 is connected by lead 11' to one end of an annular resistance bank 72desirably mounted on an insulating panel 34 associate with Wheatstonebridge l3.

The drum 33 associated with Wheatstone bridge 64 mounts a pair of spacedwiper arms 14 and I5 insulated from each other and designed-to contactresistance bank 66 and conducting ringv 61; and resistance bank 68 andconducting ring 69, respectively. Thus, depending upon the position ofthe drum 33 and the wiper arms 14 and 15, a predetermined amount ofresistance banks 66 and 68 will be placed in circuit.

Also mounted on panel 34 of bridge 73, concentric with resistance 12 isa conducting ring 16 connected by lead H to movable arm 18 of multiplierswitch 79. Switch 19 has a plurality of fixed contacts 8i which may beselectively engaged by said movable arm 18. One of the fixed contacts 8|is connected by lead 82 to common lead 83 and each of the other fixedcontacts 8! has a resistance connected thereto at one end and designated84a, 84b. etc. The other end of said resistances 84 is connected tocommon lead 83 which is in turn connected by lead 85 to point 23 ofWheatstone bridge 13. The drum 33 9 of said bridge 13 carries a wiperarm 86 which is designed to contact resistance bank 12 and conductingring 16 so that depending upon the position of drum 33 a predeterminedamount of resistance bank 12 will be placed in circuit.

Point 24 of bridge 13 is connected by lead 81 ,to one end of annularresistance bank 88 mounted on panel 34 associated with bridge 89. Alsomounted on panel 34 concentric with resistance bank 88 is a conductingring 9 I, a second annular resistance bank 93 and associated conductingring 92 and a third annular resistance bank 95 and associated conductingring 94. The conducting rings 9I, 92 and 94 are desirably connected topositive main 59. One end of annular resistance bank 93 is connected bylead 96 to point 24 of Wheatstone bridge 89. One end of annularresistance bank 95 is connected by lead 91 to point 24 of Wheatstonebridge 98.

The drum 33 associated with bridge 89 desirably mounts threelongitudinally spaced wiper arms 99, I M and I02 insulated from eachother and designed respectively to contact annular resistance bank 95and conducting ring 94; annular resistance bank 93 and conducting ring92 and annular resistance bank 80 and conducting ring 9|. Thus dependingupon the position of drum 33, a predetermined amount of resistance banks95, 93 and 88 will be placed in circuit.

The circuit also includes three Wheatstone bridges I 03, I04 and I eachof which has an associated panel 34. Each panel 34 mounts respectivelyan annular resistance bank I06, I01 and I 08 concentric with conductingrings I09, I I I and H2 respectively, a second annular resistance bankH3, H4 and I I5 and a second conducting ring H6, H1 and H8 respectively.The drum 33 associated with each of said Wheatstone bridges I03, I04 andI05 mounts a pair of spaced wiper arms II9, I2I; I22,I23 and I24, I25respectively. Each of the wiper arms contacts both a resistance bank anda conducting ring. Arms I I 9 and I2I contact resistance bank I06 andconducting ring I09; resistance bank I I3 and conducting ring II6respectively. Arms I22 and I23 contact resistance bank I01 andconducting ring III; resistance bank H4 and conducting ring II1respectively. Arms I24 and I25 contact resistance bank I08 andconducting ring II2; resistance bank H5 and conducting ring II 8respectively. Thus, depending upon the position of the drum associatedwith said bridges I03, I04 and I05, the Wiper arms carried thereby willplace a predetermined amount of the associated resistance banks incircuit.

One end of resistance bank II5 of bridge I05 is connected by lead I26 tothe point 23 of bridge 89. The end of the associated resistance bank I08is connected by lead I21 to point 24 of said brdige I05. The other point23 of said bridge I05 is connected by lead I28 to movable arm I29 ofsection C of aircraft selector switch I3I. Switch I3I desirably has twoother sections, i. e., sections A and B, said sections A, B and C beingassociated respectively with the nose wheel and the two main wheels ofthe aircraft.

Each of the sections A and B also has a movable arm I32 and I33respectively, said arms being ganged together with movable arm I29 ofsection C and with the movable arm 18 of multiplier switch 19 so thatsaid arms will move in unison upon setting of the knob I34 to theaircraft type position.

Each of the sections A, B and C of switch I3I has a plurality of fixedcontacts I35 which may be selectively engaged by the associated movablearms I32, I33 and I29 respectively. Each section has a plurality ofresistances, two of which are illustratively shown and designated I36and I31, connected respectively at one end to an associated contact I35. The other ends of said resistances are connected to an associatedcommon lead I38, I39 and I4I respectively.

Common lead I4I of section C of switch I3I is connected by lead I 42 toone end of resistance 56, the movable arm 46 of which is connected bylead I43 to positive main 59. Point 23 of Wheattone bridge I03 and point24 of Wheatstone bridge I04 are connected by leads I44 and I45respectively to movable arms I32 and I33 of sections A and B of switchI3I. The common leads I38 and I39 of said sections A and B are connectedby leads I46 and I41 respectively to one end of resistances 49 and 53,the movable arms 39 and 43 of which are connected to positive main 59 asby leads I48 and I 49 respectively.

The conducting rings I09, III and H2 of the bridges I03, I 04 and I05are connected by leads I5I, I52 and I53 respectively to positive main 59and conducting ring II 6 of bridge I03 is also connected to positivemain 59. One end of resistance bank I06 of bridge I03 is connected bylead I54 to point 24 of said bridge. One end of resistance bank II3 ofbridge I03 is connected by lead I55 to conducting ring II1 of bridgeI04. One end of resistance bank I01 of bridge I04 is connected by leadI56 to point 24 of said bridge I04, and one end of resistance bank H4 isconnected by lead I51 to conducting ring II8 of bridge I05.

The movable arm 4| of one of the scales (Fig. 2), i. e., scale 35associated with the nose weight, is connected by lead I58 to positivemain 59. One end of resistance bank 5I is connected by lead I59 tomovable arm 44 of scale 36 and one end of resistance bank 54 isconnected by lead I6I to movable arm 41 of scale 31. Thus the resistancebanks 5|, 54 and 51 are connected in series and one end of resistancebank 51 is connected by lead I62 to point 23 of Wheatstone bridge I63.

Point 24 of bridge I 63 is connected by lead I64 to movable arm I65 offuel consumption switch I66, said movable arm being controlled by meansof a knob I61. The switch has a plurality of fixed contacts I68, one ofwhich is directly connected to common lead I69 and the others of whicheach has the end of a resistance I1I afiixed thereto respectively, withthe other ends of said resistances being connected to said common leadI69. Although any number of resistances I1-I could be provided,depending upon the number or increments of weight relating to fuelconsumption, but two resistances I1Ia and I1Ib are illustrativelyidentified.

Common lead I69 of switch I66 is connected by lead I 12 to one end ofannular resistance bank E13, desirably mounted on panel 34 of bridgeI63. Also mounted on panel 34 concentric with resistance bank I 13 is aconducting ring I14, a second annular resistance bank I15 and a secondconducting ring I16. The conducting rings I14 and I16 are both desirablyconnected to positive main 59 and one end of resistance I15 is connectedby lead I11 to one end of an annular resistance bank I18 mounted on apanel 34 associated with Wheatstone bridge I19. The drum 33 associatedwith bridge I63 mounts a pair of spaced wiper arms I8I and I82 insulatedfrom each other and contacting resistance bank I 13 and conducting ringI14; and resistance bank 11 135 and conducting ring I 16 respectively.Thus, depending upon the position of drum 83 and wiper arms I84 and.l.82 ,-.a;predetermined amount of resistance banks I13 and L15 will beplaced in circuit.

Also mounted on panel .34 of bridge HQ concentric with resistance bankI18 is a conducting ring I83 connected by lead .134 to movable arm 185of multiplier switch .1855 which is identical to multiplier switch 19,corresponding parts having the same reference numerals primed, said .arm185 being ganged to move in unison with arm 18 f switch 19 upon rotationof knob 534. The common lead .33 .of switch 1.86 is connected by lead481 to point .23 :of Wheatstone bridge H9.

The drum 33 of bridge .113 carries a wiper arm IE8 contacting resistancebank I18 and conducting ring .183 so that depending upon the position ofthe drum and the wiper arm I38, a predetermined amount of resistancebank 5.13 will be placed in circuit. Point 24 of bridge 19 is connectedby lead I89 to one end of annular resistance bank 19-1 mounted on "panelof bridge 98. Also mounted on panel 3 concentric with resistance 19-! isa conducting ring 1.92, a second annular resistance bank .193 and asecond conducting ring I94.

The conducting rings I82 and i914 are both connected to positive main59. One end of resistance bank I93 is connected by lead W to movable arm1.93 of a second aircraft selector switch E91, said arm .5 93 beingganged to move in unison with the arms of selector switch I3! uponsetting of the latter by control knob 1:34.

Switch 31 has a plurality of fixed contacts I38 which may successivelybe engaged by mov-= able arm 1%. The contacts 98 are connectedrespectively .by a plurality of leads I98 to the movable arms .29! of afuel moment switch 202. This switch has a plurality of sectionscorresponding to the number of types of aircraft to be measured by theequipment, two sections A and B being i'llustratively shown, each havinga movable arm 2M ganged to move in unison with the. movable arm I65 offuel consumption switch I66.

Each of the sections of switch 2% has a plurality of fixed contacts 283which may selectively be engaged by the associated movable arms 2M. Oneof the fixed contacts is directly connected to an associated common leadand each of the other fixed contacts has a resistance connected theretoat one end, two resistances 295a, 285 being illustratively designated.The

free end of the resistances 2635 of each section is connected to anassociated common lead 2%, said leads being connected together by lead206, the leads 2% being connected'by lead 201 to point 23 of bridge 68.

The drum 33 of bridge 98 carries a pair of wiper arms 288, 209 insulatedfrom each other and designed to contact resistance bank [93 andconducting ring I94; and resistance bank I9! and conducting ring 192respectively so that depending upon the position of drum '33 and wiperarms 2538, 2E9 carried thereby, a predetermined amount of resistancebanks H33 and I9! will be placed in circuit.

In the circuit shown in Figs. 1 and 2, the nose of the aircraft isselected as the reference datum. The center of gravity may also bedetermined by selecting .a reference datum other than the nose of theaircraft. Thus, in the embodiment shown in Fig. .3, the main wheels areselected as the reference datum .and in such case only the moi lead 263to movable arm 253' of scale v2 51.

1-2 ment of the nose wheel :need be taken into account to determine thecenter of gravity.

The equipment shownin Fig. .3 also utilizes a plurality of substantiallyidentical Wheatstone bridge circuits. Each bridge has a pair .ofbalancing resistances 2.3.1, 23-2 connected at one end to points 233 and234 of the associated bridge with the other ends of said resistancesbeing connected to negative .main .235.

A servo-amplifier .236 connected by input leads 231 and 238respectively, to points 233 and .234 of each bridge is connected by lead239 .to a servomotor 2 1i. Motor .Z i-I is operatively connected bymeans of a shaft 241.2 to a rotatable member desirably a drum 2 33 whichcarrie Wiper arms to engage associated resistances and conducting ringsmountedon ana'ssociated upright-panelflil so that depending upon theposition .of the drum and the wiper arms, a predetermined amount ofresistance may be placed in circuit.

The equipment desirably comprises a plurality of weighing scales of anysuitable type, three weighing scales being illustratively shown,designated by the numerals 23.5, .246 and 241 to measure the weight onthe nose wheel and two main wheels respectively.

In the illustrative embodiment herein shown, scale 245 associated withthe nose wheel, controls a set of three movable contact arms '2 48, 2 19and 25! and the scales 24.6 and 241 associated with the main wheels each.controls a single movable arm 252 and 253 respectively.

The movable contact arms 24B, 249 and 25l coact with associatedresistance banks 254, 255 and 256 respectively, and movable contact arms252 and 253 coact with resistance banks 251 and 258, said movable armsplacing in circuit that portion of the associated resistance bankrelated to the value of the weight being measured. The movable arm 248of one of the scales, i. e., the scale 245, is connected by lead 259 topositive main 261. One end of resistance bank 254 is connected by lead.232 to movable arm 25-2 of scale 246 and one end of resistance bank 251is connected by Thus, the resistance banks 254, 2.51 and 258 areconnected in series.

One end of resistance bank 258 is connected by lead 234 to point 233 ofWheatstone bridge 265. Point 234 of bridge 26.5 is connected by lead 263to one end of an annular resistance bank 261 desirably a continuouslength of Wire mounted on supporting panel 244. Also mounted on panel.244 concentric with resistance bank 261 is a conducting ring 268, asecond annular resistance bank 269 and associated conducting ring 21]and a third annular resistance bank 212 and associated conducting ring213. The conducting rings 268., 211 and 213 are desirably connected topositive main 261. One end of resistance bank 269 is connected by lead214 to one end of an annular resistance bank 215 desirably mounted oninsulating panel 2% associated with Wheatstone bridge 216 and one end ofresistance .bank 212 is connected by lead 211 to point 233 of Wheatstonebridge 218.

The drum 2433 associated with bridge 265 carries a plurality oflongitudinally spaced wiper arms 219, 281 and 282 insulated from eachother and designed to contact resistance bank 212 and conducting ring213; resistance bank 269 and conducting ring 2.11 and resistance bank261 and conducting ring 268, respectively. Thus, depending upon theposition of drum 243 and the wiper arms 219, 28! and 282, apredetermined amount of the 13 associated resistance banks will beplaced in circuit.

Also mounted on panel 244 of bridge 216 concentric with annularresistance 215 is a conducting ring 283 connected by lead 284 to point233 of bridge 216. Point 234 of bridge 216 is connected by lead 285 tocommon lead 286 of aircraft selector switch 281. The switch 281 has aplurality of fixed contacts 288 which may be selectively engaged by amovable contact arm 289 controlled by a suitable knob 291. Each fixedcontact has a resistance 292 connected at one end thereto respectively,the other ends of said resistances being connected to common lead 286.In the illustrative embodiment herein, two resistances 292 aredesignated 292a, 29212.

Movable arm 289 is connected by lead 293 to one end of resistance 255,the movable scale arm 249 engaging said resistance being connected topositive main 261.

The drum 243 associated with bridge 218 desirably carries a wiper arm294 designed to contact resistance bank 215 and conducting ring 283 sothat depending upon the position of drum 243 and wiper arm 294, apredetermined amount of resistance bank 215 will be placed in circuit.Point 234 of bridge 218 is connected by lead 295 to common lead 296 offuel consumption switch 291. Switch 291 has a plurality of fixedcontacts 298 which may selectively be engaged by movable arm 299. One ofthe fixed contacts 298 is directly connected to common lead 296 and eachof the other fixed contact 298 has one end of an associated resistance301a, 301b, etc. connected thereto respectively, the other ends of saidresistances being connected to common lead 296.

Movable arm 299 is connected by lead 302 to one end of annularresistance bank 303 mounted on panel 244 of bridge 218. Also mounted onpanel 244 concentric with resistance bank 303 is a conducting ring 304,a second annular resistance bank 305 and a second conducting ring 306.The conducting rings 304 and 306 are both desirably connected topositive main 261 and one end of resistance bank 305 is connected bylead 301 to one end of annular resistance bank 308 mounted on panel 244associated with bridge 309. Drum 243 of bridge 218 desirably mounts apair of wiper arms 311 and 312 insulated from each other and designed tocontact resistance bank 303 and conducting ring 304; and resistance bank305 and conducting ring 306 respectively so that depending upon theposition of said drum and the wiper arms 31 I, 312, a predeterminedamount of the associated resistance banks will be placed in circuit.

Also mounted on panel 244 of bridge 309 concentric with resistance bank308 is a conducting ring 313 connected by lead 314 to point 233 ofbridge 309. Point 234 of bridge 309 is connected by lead 31 to one endof annular resistance bank 316 mounted on panel 244 of bridge 311.

Drum 243 of bridge 309 carries a wiper arm 318 engaging resistance 308and conducting ring 313 so that depending upon the position of the drumand the wiper arm, a predetermined amount of resistance 308 will beplaced in circuit.

Point 234 of bridge 31'! is connected by lead 319 to movable arm 321 ofa selector switch 322, said movable arm 321 being ganged with movablearm 289 of switch 281 and controlled by knob 291. Arm 321 is designedsuccessively to engage a plurality of fixed contacts 323 connectedrespectively to the leads 324 to the movable arms 325 of fuelconsumption moment switch 326, said arms 325 being ganged with themovable arm 299 of fuel consumption switch 291 so that said arms willmove in unison upon rotation of knob 321.

The switch 326 desirably comprises a plurality of sections dependingupon the number of types of aircraft to be measured by the equipment. Inthe illustrative embodiment, the switch has two sections A and B. Eachsection has a plurality of fixed contacts 328 selectively engaged by theassociated movable contact arm 325. One of the contacts 328 of eachsection is connected directly to an associated common lead 329. Theother fixed contacts of section A of switch 326 are connectedrespectively to one end of a plurality of resistances 331a, 3311), etc.,the other end of said resistances being connected to the associatedcommon lead 329. The common leads 329 are connected by lead 332 andcommon lead 329 is connected by lead 333 to one end of annularresistance bank 334 also mounted on panel 244 of bridge 311. The annularresistance banks 316 and 334 each has an associated conducting ring 335and 336 mounted on said panel 244, said conducting rings being connectedto positive main 261.

Drum 243 of bridge 311 mounts a pair of Wiper arms 331 and 338 insulatedfrom each other and designed to engage resistance bank 334 andconducting ring 336; and resistance bank 316 and conducting ring 335respectively, so that depending upon the position of the drum and thewiper arms, a predetermined amount of the associated resistance will beplaced in circuit.

The point 233 of bridge 311 is connected by lead 339 to annularresistance bank 341 mounted on panel 244 of bridge 342. Also mounted onsaid panel 244 concentric with resistance bank 341 is a conducting ring343, a second annular resistance bank 344 and a second conducting ring345. The conducting rings 343 and 345 are both connected to positivemain 251. One end of annular resistance bank 344 is connected by lead346 to point 234 of bridge 342.

Point 233 of bridge 342 is connected by lead 341 to movable arm 348 ofaircraft selector switch 349. Movable arm 348 is ganged with movable arm239 of switch 291 and with movable arm 321 of switch 322 so that saidarms will move in unison. Switch 349 is identical to switch 281 andcorresponding parts have the same reference numerals primed. Common lead286 is connected by lead 351 to one end of resistance 256, the movablescale arm 251 engaging said resistance being connected to positive main261.

Drum 243 of bridge 342 carries a pair of wiper arms 352 and 353insulated from each other and designed to engage resistance bank 344 andconducting ring 345; and resistance bank 341 and conducting ring 343respectively, so that depending upon the position of the drum 243 andwiper arms 352 and 353, a predetermined amount of resistance 344 and 341will be placed in circuit.

In'the circuits shown in Figs. 1 and 2 and in Fig. 3, but three weighingscales are provided. In the circuit shown in Fig. 4, four weighingscales 3'61, 362, 353 and 364 are provided which are so spaced that anyone of the scales may carry the nose wheel of the aircraft to bemeasured and two of the remaining three scales will carry the two mainwheels. Thus, the aircraft may be so positioned on the scales that it isat substantially right angles to the direction of the wind, to minimizethe effect thereof on the weight of the aircraft as indicated by thescales.

The circuit shown in Fig. 4 utilizes a pair of substantially identicalWheatstone bridge circuits. Each bridge has a pair of balancingresistances 362 and 383 connected at one end to points364 and 365 of theassociated bridge with the other ends of said resistances beingconnectedto negative main 388.

A servo-amplifier 367, connected by input leads 368 and 389 respectivelyto points 364 and 365 of each bridge, is connected by lead 37! to aservomotor 372. Motor 372 is operatively connected by means of a shaft373 to a rotatable member, desirably a drum 374 which carries wiper armsto engage associated resistances and conducting rings mounted on anassociated panel 375 so that depending upon the position of the drum andthe wiper arms, a predetermined amount of resistance may be placed incircuit.

In the illustrative embodiment, the scales 35!, 362, 363 and 354 eachcontrols a pair of movable contact arms 379, 377; 378, 379; 38!, 382 and383, 384, respectively. The contact arms 376, .379, 38! and 383 coactwith associated resistance banks 385, 386, 387 and 388 respectively andthe contact arms 877, 379, 392 and 384 coact with associated resistancebanks 389, 39!, 392 and 393 respectively, said movable arms placing incircuit that portion of the associated resistance bank related to thevalue of weight being measured.

One end of resistance bank 389 is connected to positive main 394. Themovable arm 37! of scale 36! is connected by lead 395 to one end ofresistance bank 39!. The movable arm 379 of scale 362 is connected bylead 398 to one end of resistance bank 392. The movable arm 382 of scale363 is connected by lead 397 to one end of resistance bank 393. Thus,the resistance banks 389, 39!, 392 and 893 are connected in series.

The movable arm 384 of scale 394 is connected by lead 398 to point 364of Wheatstone bridge 399. Point 365 of bridge 399 is connected by lead40! to one end of annular resistance bank 492 mounted on panel 375 ofbridge 399. Also mounted on panel 375 concentric with resistance bank402 is a conducting ring 403, a second annular resistance bank 494 and asecond conducting ring 405. The conducting rings 493 and 445 are bothdesirably connected to positive main 394. One end of annular resistancebank 464 is connected by lead 406 to one end of annular resistance bank407, desirably mounted on insulating panel 375 associated with bridge408.

The drum 374 associated with bridge 399 carries a pair of Wiper arms 499and 4!! insulated from each other and designed to contact resistancebank 402 and conducting ring 493; and resistance bank 494, andconducting ring 405, respectively. Thus, depending upon the position ofdrum 374 and wiper arms 409 and 4! I, a predetermined amount of theassociated resistances will be placed in circuit.

Also mounted on panel 375 of bridge 408 concentric with resistance bank407 is a conducting ring 4l2 connected by lead 413 to point 365 ofbridge 408. The drum 374 associated with bridge 408 carries a wiper arm414 designed to contact resistance bank 407 and conducting ring 4!2.

Thus, depending upon the position of drum 374- and wiper arm 4!4 apredetermined amount of resistance 40'! will be placed in circuit.

One end of each of the resistance banks 385, 386, 387 and 388 isconnected to positive main 394. The movable arms378, 378, 38! and 383associated with said resistance banks respectively, are connected tofixed contacts 4L5, M6, M7 and 4! 8 of relays M9, 42!, 422 and 423respectively. The movable arms 424, 425, 426 and 427 of said relays areconnected together by lead 428, which;

in turn is connected to movable arm 429 of aircraft selector switch 43!.

' Ann 429 selectively engages a plurality of fixe contacts 432 connectedrespectively to one endof a plurality of resistances 433, 434, etc, the.other end of said resistances being connectedto common lead 435 which isconnected by lead 436 to point 364 of bridge 408.

The scales 36!, 362, 363 and 364 each controls a normally openmicro-switch 437, 438, 43.9.;and 44! respectivedly, the movable contactarms 442,- 443, 444 and 445 of which are connected to'positive main 394.The fixed contacts 448, 447, 448 and 449 of said micro-switches areconnected respectively by leads 45!, 452 and 453 and 454 to one side ofthe coils 455, 456, 457 and 458 of relays 459, 46!, 462 and 463, theother side of said coils being connected to negative main 366.

The relay 459 has a fixed contact 464 and a movable contact arm 485normally spaced therefrom; the relay 46! has a pair of fixed contacts466, 487 each having a movable contact arm 468, 459 normally spaced fromthe associated fixed contact and ganged to move in unison; the relay 462has three fixed contacts 47!, 472, 473, each having a movable contactarm 474, 475, 476 nor-' mally spaced therefrom and ganged to move inunison and the relay 493 also has three fixed contacts 477, 478 and 479each having a movable contact arm 48!, 482, 493, normally spacedtherefrom and ganged to move in unison.

Fixed contact 484 of relay 459 is connected to positive main 394.Movable arm 465 is connected by lead 484 to fixed contact 488 of relay46! and by leads 434, 485 to fixed contact 472 of relay 462. Movable arm488 of relay 45! is connected by leads 488 and 487 to fixed contacts 477and 47! of relays 483 and 462 respectively. Fixed contact 467 of relay46! is connected to positive main 394 and movable arm 469 is connectedby lead 468 to fixed contact 473 of relay 462.

Movable arm 474 of relay 482 is connected by lead 489 to one side ofcoil 49! of relay 42!. Movable arms 475 and 476 of relay 462 areconnected by leads 492 and 493 to fixed contacts 478 and 479 of relay463. Movable arms 48!, 482 and 483 of relay 463 are connected by leads494, 495 and 496 respectively to one side of coils 497, 498 and 499 ofrelays M9, 422 and 423 and the other side of coils 497, 49!, 498 and 499are connected to negative main 368 to complete the circuit.

Calculation of resistances In determining the value of the resistancesutilized in the circuits above described, the following limits for theequipment will be assumed.

- To determine the value of the resistance banks 49, 53, 56 of Figs. 1and 2; resistance banks 255 Right Main Whee1.

III

weightogLpounds Min. Log. Res. Max. Log.

Nose Wheel 4, Left Main Wheel.. 15, Right Main Wheel 15,

Thus, the value of resistance banks 49, 255 and 256 will be from 3,602ohms to 4,031 ohms and the value of resistance banks 53 and 56 will befrom 4,176 to 4,845 ohms.

For the circuit shown in Fig. 4, as any one of the scales can carry thenose wheel or a main wheel, the resistance banks 385, 386, 381 and 388must cover the range between the minimum weight of 4,000 pounds and themaximum weight of 70,000 pounds and the value of each of such resistancebanks is from 3,602 ohms to 4,845 ohms.

Each 100 pounds of weight to be applied to the scale associated witheach resistance is made to correspond to one ohm of resistance inascertaining the value of the resistance banks 48, 52, 55 and 54, 51 ofFigs. 1 and 2; resistance banks 254, 251, 258 of Fig. 3 and resistancebanks 389, 39I, 392, 393 of Fig. 4.

For the circuits shown in Figs. 1 and 2 and in Fig. 3, th followingtabulation can be made:

Weight in Pounds on Min.

Res. Max.

Thus, the value of resistance banks 48, 5I and 254 will be from 40 to200 ohms, and the value of resistance banks 52, 55, 54, 51, 251, 258will be from 150 to 700 ohms.

For the circuit shown in Fig. 4 as any one of the scales can carry thenose wheel or a main wheel, the resistance banks 339, 39I, 392 and 393must cover the range between the minimum weight of 4,000 pounds and themaximum weight of 70,000 pound and the value of each of such resistancebanks is from 40 to 700 ohms.

To determine the values:

the logarithm of each distance is determined and multiplied by 1,000.

For the circuit shown in Figs, 1 and 2, the following tabulation may bemade:

Distance in Inches From Nose of Aircraft Min. Log. Res. Max. Log. Res

N osc Wheel 2.000 2, 000 2. 204 2, 204 Left Main Wheel 430 2. 633 2, 633610 2. 785 2, 785 Right Main Wheel 430 2.633 2, 633 610 2. 785 2, 785

Min Log Res Max. Log. Res.

Distance in Inches from Main Wheels to Nose Wheel 330 2. 519 2,519 4502.653 2,653

Thus, the values of resistances 292a and 433 is 2,519 ohms and the valueof resistance 292b and 434 is 2,653 ohms.

With the nose of the aircraft as the reference datum, as is used in thecircuit shown in Figs. 1 and 2, the moments about the nose due to theweight on the nose wheel and each of the two main wheels may bedetermined by multiplying the weight on the wheel by its distance fromthe nose of the aircraft and the total moment may be found by adding theindividual moments.

The logarithm of the individual moments may be found by adding thelogarithms of the weight on the wheel and the logarithm of the distanceof such wheel from the nose of the aircraft and such logarithm ismultiplied by 1,000. The following tabulation may be made:

VII

Logarithm of Monlem Minimum Maximum Nose Wheel (s. (s%2+2.000) 1,000=(4.30l+2.204) l,000=

Wheel. 6,809 7,630

Thus the value of resistance banks I 06, I01 and I08 of bridges I03, I04and I05 respectively, as-

sociated with the nose wheel moment and each of the two main wheelmoments is from 5,602 to 6,505 ohms and from 6,809 to 7,630 ohmsrespectively.

In determining moments, if 10,000 inch/pounds is made to correspond toone ohm, the value of resistance banks II3, H4 and H5 of bridges I03 I04and I05 of Fig. 1 may be determined as follows:

Thus, the value of resistance bank H3 is from to the maximum sum of suchweights.

40 to 320 ohms and the values of each resistance bank H t and H is from645 to 4,270 ohms.

' As the resistance banks 334 of bridgetll and resistance bank GM ofbridge 002 of Fig. 3 respond respectively to the take 01f moment andlanding moment and as the minimum moment of the circuit shown in Fig. 3is equal to 330 times 4,000 or 1,320,000 and the maximum moment, 450times 20,000 or 9,000,000 and since 10,000 inch pounds corresponds tooneohm, the value of resistance banks 330 and 3 3i is from 132 to 900 ohms.

To find-the sum of the individual moments due to the weight on the nosewheel and each of the two main wheels, the individual moments are addedby connecting the resistances I I3, I i4 and H5 in series in Figs. 1 and2. The resistance bank 03 of bridge 89 covers the range from the minimumto the maximum sum of the moments divided by 10,000. Thus the minimummoment is equal to 1,330 ohms and the maximum moment is equal to 8,860ohms and the value of resistance bank 03 on bridge 80 is from 1,330 to8,860 ohms.

The resistance banks 08 and% of bridge 89 and resistance bank i923 ofbridge 90 of Figs. 1 and 2 extend from the logarithm multiplied by 1,000of the minimum'total moment to that of the maximum total moment. Thefollowing tabulation may be made:

Minimum moment=400,000 +6,450,000+ 6,450,000 =13,300,000 1,00010g.13,300,000:7,124

Maximum moment 3,200,000+.42,700,000+42,-

700,000=88,600,000 1,000 log.88,600,000=7,947

Thus, the value of resistance banks'SS, 95 and [.03 is from 7,124 to7,947 ohms.

The resistance banks 340 and 310 of bridges 342 and 3!? of Fig. 3 extendfrom the logarithm times 1,000 of the minimum total moment to that times1,000 of the maximum total moment. The following tabulation may be made:

Minimum 'moment=330 i,000=1,320,000 1,000 l0g.1,320,000:6,121 Maximummoment=4=50 20,000=9,000,000 1,000 1og.9,000,000:6,954i

Thus, the value of resistance banks 344 or 316 extends from 6,121 to6,954 ohms.

To determine the sum of the weights onthe nose wheel and the two mainWheels, the resistances associated with such weights are connected inseries. The value of resistance bank 06 of bridge 0 and resistance bankI13 of bridge m3 of Figs. 1 and 2, of resistance bank 267 and 2l2 ofbridge 205 and resistance bank 303 of bridge 278 of Fig. 3 and ofresistance bank 402 of bridge 399 of Fig. 4 extends from the minimum Ifeach 100 pounds of weight to be applied to the scale associated witheach resistance is made to correspond to one ohm of resistance, we find:

Weight on Minimum Maximum Nose Wheel 4, 000 20, 000 Left Main Wheel 15,000 70, 000 Right Main Wheel 15, 000 70, 000

Total minimum Weight divided by l00=340.

Total maximum weight divided by l00=1,600.

Thus, the value of resistance banks 06, 13,261, 212, 303 and 302 is from340 to 1,600 ohms.

The value of resistance bank 08 of bridge .64, and resistance bank [15of bridge E03 of.Figs. land .2; of resistance bank 250 'of bridge 5.20.5and resistance bank 305 of bridge 2'88 oftliig. 3 and of resistancebank304 of bridge 300 ofFig. 4 is determined by. ascertaining thelogarithmof the minimum total weight and maximum total weights andmultiplying such logarithm by 1,000.

XII

Log. Res

Weight Minimum: 34,000 4. 531 4, 531 Weight Maximum: 160, 000 .i 5. 2045, 204

Thus, the values of resistancebanks 68, [75, 209, 305 and 404i is from4,531 to 5,204 ohms.

The resistances Illa, IHb of fuel consumption switch its of'Figs. 1 and2, and resistances sew and 3017) of fuel consumption switch 291 of Fig.3 are related to predetermined amountsof fuel consumed. Thus, forexample, resistances Him and 305a are related to 500 gallons or 3,000pounds and resistances l'ilb and 30H) to 1,000 gallons or 6,000 pounds.To determinethe values of such resistances, the weight of fuel isdivided by 100. Thus, thefollowing tabulation can be made:

Fuel Consumed g g g i gi g 500 gallons 3, 000 30 1,000 gallons 6, 000 60The "resistances 205a and 2051) of sections A and B of switch 202 ofFig. 2 and the resistances 33laand33lb ofswitch 326 of Fig. 3 arerelated to predetermined momentsof the fuelconsumed.

Assuming that the nose of the aircraft has been selected as thereference datum and the average distance of the fuel is 402 inches fromthe nose for .a type A aircraft and 600 inches for a type B aircraft,the following tabulation can be made in determining the landing centerof gravity:

The values of resistance 205a of section A of .switch 202 is 1200 ohms;resistance 2051) of section A'has a value of 241.2 ohms. Resistance 205aof section B has a value of ohms and resistance "2051) of section'B hasa value of 360 ohms.

Assuming that the main wheels of the aircraft have been selected as thereference datum and the average distance of such fuel is 402 inches fromthe nose or 28 inches-from the main wheels for a type A aircraft and 600inches from the nose or inches from the main wheels for a type Baircraft, the following tabulation can be made:

The value of resistance saw of section A of switch 326 is 8.4 ohms,resistance 33Ib of section A has a value of 16.8 ohms. Resistance 36H aof section B has a value of 3 ohms and resistance 33") of section B hasa value of 6 ohms.

To determine the distance of the center of gravity of the aircraft, froma given reference datum, the total moment is divided by the totalweight. This may be expressed by the formula:

Log.CG=l og.total momentlog.total weight or Logtotal moment=log.totalweight+log.CG

The resistance banks 12 and I28 of the two bridges l3 and I 19 relatedto center of gravity extend from the logarithm multiplied by 1,000 of avalue somewhat below the minimum distance of the center of gravity fromthe reference datum to a value somewhat in excess of the maximumdistance.

As such minimum and maximum distances of the center of gravity for thetype A aircraft are 380 and 400 inches, the resistance values ofresistance banks 12 and I28 are set to a range of from 360 to 420inches. The following tabulation can be made:

XVI

Log. Res.

Minimum 0. e., 360 2.556 2,556 Maximum 0. G., 420 2. 623 2, 623 I Thus,the values of resistance bank '12 of bridge 13 and resistance bank I18of bridge I79 are from 2,556 to 2,623 ohms.

In order that the resistance banks 12 and I18 of value from 2,556 to2,623 ohms may be used to indicate the center of gravity for the largertype 13 aircraft, the followin calculations are made:

The center of the scale for the center of gravity of the type A aircraftis midway between 360 and 420, i. e., 390 inches. Let it be assumed thatthe center of the scale for the type B aircraft is 565 inches.

The logarithm of the ratio of the two centers of the scales is ohms.Similarly, the mid-point on the scale for the center of gravity of atype B aircraft is 565, the logarithm of which multiplied by 1,000 isequivalent to 2,752 ohms.

As the multiplying factor to convert the center of gravity scale from atype A aircraft to a type B aircraft is 161 ohms, this amount added tothe ohmic value of the logarithm of the selected limits of 360 and 420inches or 2,556 and 2,623 ohms respectively will give limits of 2,717and 2,784 ohms.

The anti-logarithms of such resistances divided by 1,000 is 521 and 608inches respectively. Thus, the limits of the scale for a type B aircraftis from 521 to 608 inches, which extends beyond the minimum and maximumlimits of the type B aircraft, i. e., from 545 to 585 inches.

Thus one and the same center of gravity resistance bank can be utilizedfor any of a wide variety of aircraft types by introducing theappropriate multiplying factor accordin to the principle above setforth.

Ihe drums of bridges l3 and H9 through suitable mechanical or electricalmeans may rotate a pointer P shown in Fig. '7 which has a verticallyadjustable rectangular panel 50! to the rear thereof. The panel 561desirably has a plurality of distinct scales 502 one for each of thetypes of aircraft for which the system is adapted and the panel 56l isso controlled by the control knob 534 as by a gear and rack arrangement503 as to cause the correct scale to enter into registry with thepointer P upon turning the knob to the selected type aircraft.

The indications on the scale markings may be spread over only degrees ofarc for example, to facilitate ease in reading regardless of the numberof types of aircraft to be measured by the equipment.

While it is preferred to utilize a plurality of distinct scales toindicate the center of gravity position for various types of aircraft,by introducing an appropriate multiplier factor for each type largerthan the smallest as above set forth, it is of course understood that asingle scale could be employed to cover the entire range for variousaircraft small and large with the omission of the multiplying factor.

As the distance of the center of gravity from the reference datum foundby the circuits shown in Figs. 3 and 4 is with respect to the mainwheels, the range of resistance banks 215, 308 and 401 may be equal to1,000 times the logarithms of the distances of the centers of gravitytherefrom between limits which extend beyond the minimum and maximum tobe measured, to give the range of resistance values for resistance banks215, 303 and 4H1.

As previously described, the type B aircraft has its range of center ofgravity at most 608 inches and at least 521 inches from the nose, thedistances of such centers of gravity from the main wheels being from 2to 89 inches. The type A aircraft has its range of center of gravity atmost 426 inches and at least 360 inches from the nose, the distance ofsuch center of gravity from the main wheels being from 10 to 70 inches.

As the limits of center of gravity are from 2 inches to 89 inches, thefollowing tabulation can be made:

XVII

1000 logarithm 2:301 1000 logarithm 89:1,949

Thus, the value of each resistance bank 215, 308 and 401 is from 301 to1,949 ohms and the rums associated with said resistancebanks arecalibrated from 2 to 89 inches.

.from the nose and has. a width of 197 inches, the limiting values ofMAC-are:

l0.0=0% MAC CG=%LX 100=44.2% MAC Thus, the MAC indicating scale for thetype B aircraft may be calibrated in percentages from 0 to 44.2corresponding to a range of center of gravities of from 521 to 608inches.

Operation 'I'he'basic principle of operation of the equipment will beclear from thefollowing brief description of the circuit shown in Fig.3.

The weight of the aircraft on the scales 2 35, 200 andZ-il' will placethat portion of the series connected resistance banks 250, 257, and258in circuit or" ohmic Value equal to the total weight divided by 100. Theweight resistance banks 254, 257 and 250 form oneleg of bridge 205 andthe resistance bank forms another leg of said bridge which, whenthe'bridge is balanced, is set to a resistance value corresponding tothat of the series connected resistance banks and at the same time theassociated resistance 200 is setto a value proportional to the logarithmof the Weight and is in series with resistance bank 215 of bridge 276 toform one leg of said bridge.

The resistance bank 255 controlled by nose wheel scale 2% and theresistance 292a of switch 20? in series therewith are of ohmic valuesrespectively proportional to the logarithm times 1,000 of the weight onthe nose wheel scale and the distance of the nose wheel from the mainwheel. The combined value of resistance bank 255 and resistance 202a isproportional to the logarithm times 1,000 of the moment of the nosewheel with respect to the main wheels and-such series connectedresistances form another leg of bridge 2%.

As the bridge 276 will normally be unbalanced, the motor 2 3i willrotate drum 203 until a'portion of resistance bank 275 will be placed incircuit that is equal in value to the difference between the combinedvalues of resistance bank 255 and resistance 202a; and the value ofresistance bank 200.

An indication correlated with resistance bank Bib which is theanti-logarithm of a multiple of the difference of resistance designatesthe position of the center of gravity of the aircraft as the quotient.

Specifically to illustrate the operation of the equipment abovedescribed, it will be applied to a type A aircraft of the followingpertinent specifications (a) Nose wheel 100 inches from the nose.

(1)) Main wheels 430 inches from the nose.

(0) Center of gravity limits from 380 inches to 4 0 inches from thenose.

Referring tQ Figs. land 2, the aircraft is positionedso that :its nosewheel rests upon scale and its two main wheelsrest on scales at and 37respectively. The knob 30 is turned to set the aircraft selector-switchlSi to the type A position. As a result the scale on panel (Fig. 7)associated with the type A aircraft will be moved into the range of"pointer P. The movable arms it2, E33 and I29 of sections A, B and C ofsaid switch engage the fixed contacts 435 associated with the respectiveresistances I30 and the movable arms 18 and I of multiplier switches i0and H30 engage the associated fixed contacts'ti and 8! respectively. Inaddition, the movable arm I05 'of switch [97 engages the associated'fixed contact vI98.

Each'movable arm 39,03 and 00 of-the weighingscaleswill tap off thatportion of the associated resistance banks 09,03 and '50 of ohmic valueequal to the logarithm of theweight multiplied by "1,000 as illustratedin tabulation III. Accordingly, assuming that the weight on scale 35'is10,000 pounds and the weights on'each of the scales 36 and 3'! is 30,000pounds, the values of resistance banks dfi, 53 and 00 in circuit will be4,000, 4,477 and 4,477ohms respectively. Simultaneously, the movablearms 33, 42,05 and M, 00 and ll of the scales will tap off that portionof the resistance banks 08, 52 and E0 and the resistances 5i, t l, 5-?of ohmic value equal to the weight divided by one hundred as illustratedby tabulation IV. "Thusgthe value of resistances 00 and'fil; '52 and5'0; 55 and 0?; -will'be 100, 300 and 300 ohms respectively.

The resistances E30 of sections A, B and G of selector switch [3! placedin circuit by the rotationof themovable armsiSZ, wt and 5 20 thereof forthe type A position, areassociated respectively with the distance fromthenose of the aircraft to the nose wheel and to each of the mainwheels. Such distances forthe typeA aircraft are as above noted, inchesto the nose wheel and 430 inches to each of the main wheels. The valueor" resistances l36, of sections A, B and C are equal to'the logarithmof the related distance multiplied by 1,000 as illustrated in tabulationV. Thus,

the value of resistances IE5 or sectionsA, Band C are 2,000, 2,633-and2,633'ohms respectively.

ing edge is 355 inches from the nose.

The resistance bank 09 and'resistance E30 of section A of switch it!which are connected in series from positive main 50 to point 23 form oneleg of bridge I03 and the annular resistance bank I06 on panel 30forms-another leg or" said bridge I03. As resistance bank 00 has a valueof 4,000 ohmsandresistanceiitt of section A of the switch l3! has avalue of 2,000 ohms, the total series resistance will be 6,000 ohms.Bridge I03 ordinarily will be unbalanced and current will flow throughservo-amplifier 25 to energize servomotor "3i. As a result, :drum 33will rotate until wiper arm H0 engages that portion of resistancetile-to place6;000-ohms in circuit, when servomotor 31 is de-energizedand drum 3% stops rotating. Thus, there is placed in circuit aresistance which is proportional to the logarithm of the product of theweight on the nose wheel and its distance from the reference datum.

At the same time wiper arm l2! taps off that portion of resistance bankM3 to place in circuit resistance-equal'to the actual momentof the nosewheel divided by'10,000 as illustrated in tabulation VIII rather thanthe logarithmic multiple of the moment-on resistance 100. Thus, as themoment on the nose wheel is 100 inches times 10,000 pounds, themomentdivided by 10,000 will equal 25 100 ohms which is the value ofresistance H3 placed in circuit.

The resistance bank 53 and resistance of section B of switch. I31 whichare connected in series from positive main 55 to point form one leg ofbridge E and the annular resistance bank I07 on the corresponding pan li another leg or" said bridge. The resistance bank 56 and'resistance I36of section 0 or switch set which are connected in series from positivemain 59 to point 23 form one leg of bridge H and the annular resistancebank [08 on corrcs; panel 3 4 forms another leg or said brid;-

As resistance banks 53 and 55 each 3. a of 4,777 ohms and resistances 36of and B of switch I31 each has a value ohms, the total seriesresistance or? the cor sponding legs will each be 7,411 ohms.

Bridges'lild and 105 will ordinarily be unbalanced and current willtherefore flow through the associated servo-amplifier to energize theservo-motor 31. As a result, the associated drum 33 will rotate untilwiper arms I22 and ii engage that portion of the associated resistancebanks I01 and I03 respectively to place M11 ohms in circuit whenservo-motor 3| is de-energized' and drum 33 stops rotating.

At the same time wiper arms I23 and respectively tap off that portion ofresistance banks IM'and H5 respectively, to place in circuit re sistanceequal to the actual moment of each or the main wheels divided by 10,000as illustrated in'tabulation VIII. Thus, as the moment on each mainwheel is 430 inches times 30,000 pounds, the moment divided by 10,000will equal 1,290 ohms which is the value of each of the resistancebani-1s H4 and! I5 placed in circuit.

The resistances H3, H4 and l l5 which are connected in series frompositive main to point 23 of bridge 09 form one leg of said bridge andhave a total value of 2,680 ohms. Bridge 00 will ordinarily beunbalanced and current will therefore flow through the associatedservo-amplifier 26 to energize servo-motor 3 I. As a result, drum 33will rotate until wiper arm l0! engages that portion of resistance bank03 to place in circuit 2,680 ohms, a multiple of the actual totalincrnent, when servo-motor 3! is de-energized and drum stops rotating.

At the same time wiper arm I02 will tap off that portion of resistancebank 8 5 to place circuit resistance equal to the loga ithm times 1,000of the total moments of the weights on the nose wheel and two mainwheels about the reference datum or 1,000,000 plus 12,00 plus 12,900,000or 26,800,000. The logarith of this sum times 1,000 equals 7,428 ohms ws the value of resistance bank 80 placed in crc'it.

The resistance banks 48, 52 55 v h are connected in series from positivemain to point 24 of bridge 04 have a total value of chr s as previouslypointed out, and form one leg of h be 64. Bridge 04 will be ordinarilyunbalanced and current will therefore flow through associatedservo-amplifier 26 to energize servo-motor As a result, drum 33' willrotate until wiper engages that portion of resistance to place incircuit 700 ohms, a multip .c of the actual total weight; whenservo-motor is die-energized drum 53 stops rotating.

At the same time wiper arm 75 will tap ofi that portion of resistancebank 00 to place circuit resistance equal to the logarithm a 1,000 ofthe total weight of 70,000pounds or 4,345 chins,

iii!

26 which is the value of resistance bank 03 placed in circuit.

As resistance bank 63 of bridge 64 and resistance bank 12 of bridge 13are in series and form one leg and resistance bank 02 forms another legof bridge 7 3, and as the value or" resistance 03 has been set to 4,845ohms and that bank 88 to 7,428 ohms, as above described, bridge 73 willbe vordinarily unbalanced. As a result, current will flow through theassociated servo-amplifier 20 to energize servo-motor 3i and drum 33 ofbridge 3 will rotate until wiper arm engages that portion resistancebank '12 to place in circuit the d aerence between 7,428 ohms and 845ohms, i. 2,533 ohms. Thus servo-motor 3! is deenergized and drum 33stops rotating.

Inasmuch as the resistance bank 38 is value proportional to thelogarithm the total moment and resistance bank. 6 3 is of ohmic valueproportional to the logarithm of the total weight, the value ofresistance bank T2 in circuit will be proportional to the logarithm ofthe distance of the center of gravity from the reference datum. Theanti-logarithm of resistance 72, i. e., of 2,583 divided by 1,000 is 383which is the actual distance from the reference datum of the center ofgravity or" the aircraft type A loaded as above described. The drum 33of bridge 73 rotates the pointer P shown in Fig. 7 through transmission503 to indicate such actual center of gravity position as 383 inches.

Since of of CG in percent MAC= 100 the center of gravity determinationfor the type A. aircraft above illustratively described is convertedinto percent MAC as follows:

As the take off center of gravity is within the permissible limits ofthe MAC of the type A aircraft, i. between 380 and 400 or between 15.2or 27.4%, the aircraft can take oii safely.

During flight of the aircraft, the center of gravity will shift byreason of the reduction of the moment caused by the consumption of fuel.Assuming that for a given flight the aircraft will consume 500 gallonsor 3,000 pounds of fuel, to determine the landing center of gravity or"the aircraft, it is merely necessary to turn snob it? in order to setthe fuel .surnption switch 500 to 500 gallons. As a result, the movablearm of switch (00 engages fixed contact i023 associated with resistanceiiia movable arms CG in percent MAC: l00==l'7% IllAC of sections A and Bof switch 202 w engage the contacts 203 associated with a resistance ofeach of the two sections A, B respectively.

By reason of the original setting of switch it! to the type A position,resistance of section A of switch 202 is in circuit, and thecorrespondresistance of section B is inactive. ance 2051 as indicated intabulation XIV has a value of 120.0 ohms {or a weight of 3,000 poundslocated 402 inches from'the nose of the aircraft.

As resnstance bank is identical to resistbanksfi, the associated wiperarm place in. circuit a resistance equal to that of resistance bank'03placed in circuit by its Wiper arm Gill, 1. e., 2,680 ohms, which isamultiple of the actual total moment. Resistance is connected atone endto positive main '59 and at its other end to point it of bridge andforms one leg 27 of said bridge. Resistance bank I63 on panel 34 ofbridge 08 and resistance 205a of section A of switch 202 are connectedin series between positive main and point 23 of said bridge 98 and formanother leg of said bridge.

Bridge 98 will ordinarily be unbalanced and current will flow throughthe associated servoamplifier 26 to energize servo-motor 3|. As a resultdrum 33 will rotate until wiper arm 200 engages that portion ofresistance bank I93 to place in circuit the difference between 2,680ohms (resistance bank 95) and 120.6 ohms (resistance 205a), i. e.,2,559.4 ohms which is the value of resistance bank I93 placed incircuit. When this occurs servo-motor 3| is deenergized and drum 33stops rotating.

At the same time wiper arm 208 of bridge 02 will tap off that portion ofresistance bank I91 equal to the logarithm times 1,000 of the actualremaining moment set by resistance I93, 1. e., 7,408 ohms.

The resistance banks 5|, 54 and 51 which are connected in series frompositive main 59 to point 23 of bridge I53 have a total value of 100ohms as previously pointed out and form one leg of bridge I63. Theannular resistance I13 on panel 34 of bridge I63 which is connected inseries with resistance I1Ia of syitch I66 for a fuel consumption of 500gallons or 3,000 pounds, forms another leg of said bridge.

Bridge I63 will be ordinarily unbalanced and current will flow throughthe associated servoamplifier 25 to energize servo-motor 3|. Drum 33 ofbridge I63 will rotate until Wiper arm I81 engages that portion ofresistance bank I13 to place in circuit 6'10 ohms, the differencebetween 700 ohms, the value of resistance banks 5|, 54 and 51 and 30ohms, the value of resistance I1|a. Thus, servo-motor 3| is de-energizedand drum 33 stops rotating.

At the same time wiper arm I82 will tap off that portion of resistancebank I15 to place in circuit resistance equal to the logarithm times1,000 of the weight of 67,000 pounds, i. e., the total weight of 70,000less 3,000 of fuel consumption weight, or 4,826 ohms, which is the valueof resistance bank I15 placed in circuit.

As the resistance bank I9I, which is connected to point 24 of bridge I19to form one leg of said bridge, has a value of 7,408 ohms and as theresistance bank I15 has a value of 4, 26 ohms and is in series withresistance bank I18 of bridge I13 to form another leg of said bridgeI10, bridge I19 will be ordinarily unbalanced. As a result, current willflow through the associated servoamplifier 2e to energize servo-motor 3|and drum 33 of bridge I19 will rotate until wiper arm I88 engages thatportion of resistance I18 to place in circuit 2,582 ohms, the differencebetween 7,408 and 4,826 ohms. Thus, servo-motor 3| is deenergized anddrum 33 stops rotating.

As above described with respect to resistance bank 88, the 2,582 ohms ofresistance bank I18 in circuit is equal to the logarithm times 1,000 ofthe distance of the center of gravity of the aircraft from the referencedatum when 500 gallons of fuel is consumed and the anti-logarithm ofresistance I18, i. e. of 2,582 divided by 1,000 is 382, which is thelanding center of gravity of the type A aircraft based on a fuelconsumption of 500 gallons or 3,000 pounds. Thus, the center of gravityhas moved forward one inch,

The operation of the embodiment of Fig. 3, in which the main wheels ofthe aircraft are selected as the reference datum will now be describedin connection with type A aircraft of the same speci fications andloading used in the foregoing de-' scription.

With the aircraft set upon the scales 245, 246 and 241, the aircraftselector switches 281 and 340 are set to type A position by turning knob29!. This will also set the switch 322 to the type A position shown. Asa result, the movable arms 289 and 348 of switches 281 and 349 willengage the fixed contact 288 associated with the resistances 202a and292a respectively and the movable arm 321 of switch 322 will engage thefixed contact 323 associated with the type A position.

The weight on scale 245 being 10,000 pounds and the weights on each ofthe scales 246 and 241 being 30,000 pounds, the movable arms 249 and 25Icontrolled by the nose scale 245 will tap off that portion of theassociated resistance banks 255 and 256 of ohmic value equal to thelogarithm of the weight multiplied by 1,000 as illustratively shown intabulation III. Thus, the value of each resistance bank 255, 256 incircuit will be 4,000 ohms.

Simultaneously, the movable arms 248, 252 and 253 of the Weighing scaleswill tap off that portion of the resistance banks 254, 251 and 258respectively of ohmic value equal to the actual weight divided by asillustrated in tabulation IV. Thus the valueof the resistance banks 254,251 and 258 in circuit will be 100, 300 and 300 ohms or a total of 100ohms.

The resistances 292a and 292'a placed in circuit are of ohmic valueequal to the logarithm multiplied by 1,000 of the distance between thenose wheel center and the main wheel centers along the longitudinal axisof the aircraft, as illustrated by tabulation VI. Such distance beingequal to 330 inches, the value of each resistance 262a and 232'! is2,519 ohms.

As a result of the initial setting of the equip: ment to the type Aposition, the resistance banks 254, 251 and 258 in series (100 ohms)will constitute one leg of the Wheatsone bridge 265. As the resistance261 on panel 244 forms another leg of bridge 265, the bridge 205 will beordinarily unbalanced and current will flow through the associatedservo-amplifier 236 to energize servomotor 24I. As a result, theassociated drum 243 will rotate until wiper arm 282 taps off thatportion of resistance 261 equal to 700 ohms when servo-motor 2 3i isde-energized and drum 243 stops rotating.

At the same time wiper arm 28I taps off that portion of resistance 269to place resistance in circuit equal to the logarithm times 1,000 of thetotal weight. The logarithm times 1, 00 of this sum equals 4,845 whichis the value of resistance 260 placed in circuit.

The resistance bank 255 (4, 00 ohms) and resistance 292a (2,519 ohms) ofswitch 281 which are connected in series from positive main 26! to point235 of bridge 216 form one leg of said bridge and have a total value of6,519 ohms and the resistances 263' and 215 which are also connectedinseries form another leg of bridge 216.

As the value of resistance bank 263 has been set to 4,845 ohms, as abovedescribed, bridge 216 will be ordinarily unbalanced. As a result,current will flow through the associated servo-amplifier 236 to energizeservo-motor 24! and drum 243 of bridge 215 will rotate until wiper arm254 engages that portion of resistance bank 215 to place in circuit1,674 ohms, the difierence between 6,5l9 and 4,845 ohms. At this timeservo-

